1. Field of the Invention
The present invention relates to a method and apparatus for estimating a length of a channel in a wired communication system, and more particularly, to a method and apparatus capable of effectively estimating a length of a channel, such that a receiver can timely trigger a high-pass filter, to reduce error propagation and enhance reception efficiency.
2. Description of the Prior Art
In a wired communication system, a channel between a transmission terminal and a reception terminal is established upon a physical cable. Therefore, the communication quality is affected by the material, length, anti-noise ability of the cable. For example, in Gigabit Ethernet, a receiver selects a proper filter or algorithm according to a length of a cable, to reduce the possibility of error propagation in an equalizer, and enhance efficiency. Therefore, how to correctly estimate the cable length has become an important factor in Gigabit Ethernet.
For Gigabit Ethernet, there are two widely used methods for estimating a cable length. One is sending a pulse signal and estimating the cable length according to a round trip time of the signal or received signal energy. Such a method needs to send the extra pulse signals, and has less estimation accuracy under some circumstances, e.g. when power is too high or too low. The other method is determining the cable length according to parameters of a digital equalizer after the equalizer completely converges. In other words, if the equalizer undergoes error propagation, the cable length cannot be estimated.
Besides, the spectrum of received signals varies with the cable length, and another conventional method uses this phenomenon to determine the cable length in the Gigabit Ethernet system. Since a low frequency portion of the received signals is interfered with direct current (DC) signals in circuits, while a high frequency portion is affected by noise, both high-frequency and low-frequency responses are not suitable for estimating the cable length, and 6 MHz and 43 MHz are selected. However, to accurately calculate signal portions at 6 MHz and 43 MHz needs to perform complicate Discrete Fourier Transform, which involves a lot of multiplication and addition operations, leading to large circuit area and high production cost, difficult to meet practical requirement.
Therefore, the conventional methods for estimating the cable length in Gigabit Ethernet need to be improved.